Printed circuit boards (PCBs) have revolutionised the electronics industry, but they lack the strength of the old hard-wired, steel-chassis devices, so it's important to handle them carefully. Although it's sometimes possible to repair a broken PCB, it can be an extremely frustrating process. Usually, the hardest part of the repair is locating all of the cracked copper traces on the circuit board (See Tips).
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Things you need
- Digital multimeter
- Nonconductive epoxy
- Razor knife
- Fine-grit emery cloth
- 35-watt soldering iron/pencil
- Soldering sponge
- Rosin core solder
- 18-gauge bare copper wire
- Wire cutters
Mix the epoxy according to the manufacturer's instructions, and apply it sparingly to one side of the PCB. Press the two halves of the broken board together, and hold them until the epoxy takes hold. The epoxy will set in a few seconds, but you should wait for thirty minutes before proceeding to the next step. (Note: If you have a two-sided board the same steps apply, but if you have a multilayered board, where all the traces are not accessible, you will have to replace the board.)
Cut through the broken copper traces using a razor knife. Remove all of the loose traces, and then carefully use the emery cloth to sand the traces from which you removed the loose sections. Sand the ends of these traces until the bright copper shows clearly. Avoid touching any of the traces that didn't break when the board broke.
Plug the soldering pencil into a 110-volt receptacle and wait for it to get hot. Clean the hot soldering tip by wiping it on a wet soldering sponge. Make sure to remove all the dirt and oxidation from the tip.
Apply a fresh "tinning" coat of rosin-core solder to the clean soldering pencil tip. A properly tinned tip will be a bright silvery colour. If the tip is a dull grey colour, you will need to repeat steps 3 and 4 until you achieve a properly tinned tip. This is necessary for the efficient transfer of heat during the soldering process.
Apply the rosin-core solder to the bared copper traces on the printed circuit board. Use care to apply no more heat than is necessary to melt the solder. Too much heat will cause the copper traces to separate from the board.
Cut pieces of the 18-gauge copper wire that are long enough to span the cut traces, and tin these short lengths of wire with rosin-core solder.
Pick up a piece of tinned wire with the tweezers and lay it carefully across one of the traces where you removed a loose section. With the piece of wire lying across the gap, touch the soldering pencil's tip to the top of the wire until it fuses to a copper trace on the board. Repeat this step with the remaining wires.
Reassemble the device and test it to see if it works properly. if the device doesn't function as it should, check your repair job by taking meter readings from the next point on the circuit breaker on each side of the repair. This will show any faulty solder connections.
Tips and warnings
- The easiest way to identify broken traces is to use a digital multimeter and take readings between adjacent terminal points on the board. Simply set the multimeter to the "Ohms" function and touch the probes to the traces. A bad trace will show as an "O.L." on the multimeter. A good trace will read 0.00 to 0.5.
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